Although it will become evident to those skilled in the art that the present invention is applicable to a variety of implantable medical devices utilizing pulse generators to stimulate selected body tissue, the invention and its background will be described principally in the context of a specific example of such devices, namely, cardiac pacemakers for providing precisely controlled stimulation pulses to the heart via an external connector assembly having lead-receiving receptacles. The appended claims are not intended to be limited, however, to any specific example or embodiment described herein.
Cardiac pacemakers, and other implantable medical devices such as cardiac defibrillators, are hermetically packaged to isolate the device from the body environment. Such devices require that electrical signals be passed between the packaged device and its external connectors, without compromising the hermeticity of the package. Depending on the configuration of the implantable device, there may be multiple electrical paths required between the device and its external connectors. These paths must be electrically and mechanically integrated with the device to provide a safe, long-term arrangement which does not compromise the hermetic package.
Typically, electrical coupling between the electronic circuits of the implantable device and the external connections provided by a connector assembly mounted outside of the implantable device are provided by a feedthrough assembly. The feedthrough assembly extends through the hermetically sealed outer wall of the device and into the connector assembly so as to couple the electronic circuits within the implantable device to lead-receiving receptacles within the connector assembly. Common feedthrough assemblies contain a number of wires equal to the number of electrical paths required for the configuration. The wires are placed in a ceramic sleeve and are sealed and mechanically secured to the sleeve, such as by brazing. The ceramic sleeve is secured to a weld ring, such as by brazing, following which the weld ring is integrated into the housing wall of the implantable device, such as by laser welding. The resulting feedthrough assembly has many individual seals and exposed lengths of wire.
Feedthrough assemblies of the type described have a number of potential problems. One such problem results from the large number of seals required. Because the plurality of wires and the weld ring each require a separate seal, the large number of seals increases the chances of a compromised seal and the resulting loss of hermeticity. Moreover, the exposed wires act as an antenna for environmental noise sources. Such noise compromises the quality of the signal transmitted, and this can lead to misinterpretation by the implantable device. Additionally, the wires can be damaged by misalignment or bending during handling of the feedthrough assembly.
It would therefore be desirable to provide a feedthrough assembly which eliminates the use of wires, reduces the number of seals required so as to reduce the potential for lost hermeticity, and eliminates the possibility of wire misalignment or bending during the handling.
It would furthermore be desirable to provide a feedthrough assembly which incorporates electric field shielding to protect the electrical paths from potential noise sources, and thus potentially inaccurate signals.
It would still furthermore be desirable to provide a feedthrough assembly which integrates signal filtering within the assembly itself, so as to focus the spectrum of frequencies to be interpreted by the implantable device.